JP6265597B2 - Biodegradable foam with improved dimensional stability - Google Patents

Description

  The present invention relates to foaming agent formulations for low density foams, methods of making them, and methods of using them.

Carbon dioxide (CO ₂ ) is used as a common blowing agent for producing foamed thermoplastics or polymer foams. In particular, carbon dioxide is recognized as an environmentally acceptable blowing agent because it has inert properties and a low global warming potential (GWP). However, there is a limit to carbon dioxide and other commonly used blowing agents, especially in the production of low density foam. Low density foams often have the problem of unacceptable post-production cell collapse. In other words, the foam structure, for example, a closed cell, shrinks and the foam volume decreases. This phenomenon may be due in part to the rapid diffusion of carbon dioxide or other blowing agents from the foam product. Therefore, carbon dioxide and other common blowing agents are often limited to the purpose of foaming high density foams with sufficient mechanical strength to minimize or prevent foam cell collapse. Is done. Alternatively, additives may be used, or improvements may need to be made to maintain or improve the dimensional stability of the low density foam in the polymer structure.

  It has been found that the composition of the present invention provides a low density foam with improved dimensional stability and does not require modification to the polymer or addition of additives. Embodiments of the present invention include such compositions, methods of making the compositions, and methods of using the blowing agents.

  In embodiments of the invention, the blowing agent composition comprises carbon dioxide and a halogenated blowing agent such as hydrofluorocarbon, hydrochlorofluorocarbon, hydrofluoroether, hydrofluoroolefin, hydrochlorofluoroolefin, hydrobromofluoroolefin, hydro A co-foaming agent selected from the group consisting of fluoroketones, hydrochloroolefins, and fluoroiodocarbons, alkyl esters such as methyl formate, water, and mixtures thereof.

  In yet another embodiment of the present invention, a foamable, biodegradable or biorenewable resin composition and carbon dioxide and a halogenated blowing agent such as hydrofluorocarbon, hydrochlorofluorocarbon, hydrofluoroether, A co-blowing agent selected from the group consisting of fluoroolefins, hydrochlorofluoroolefins, hydrobromofluoroolefins, hydrofluoroketones, hydrochloroolefins, and fluoroiodocarbons, alkyl esters such as methyl formate, water, and mixtures thereof. A biodegradable or biorenewable foam is formed from the included blowing agent composition.

  In yet another embodiment of the present invention, a method of making a blowing agent composition comprises carbon dioxide and a halogenated blowing agent such as hydrofluorocarbon, hydrochlorofluorocarbon, hydrofluoroether, hydrofluoroolefin, hydrochlorofluoroolefin. , Hydrobromofluoroolefin, hydrofluoroketone, hydrochloroolefin, and fluoroiodocarbon, alkyl esters such as methyl formate, water, and co-blowing agents selected from the group consisting of mixtures thereof.

  In yet another embodiment of the present invention, a method of making a low density foam using a blowing agent composition includes the following steps: (a) mixing a blowing agent and a foamable resin; The step of forming an expandable resin composition, wherein the blowing agent includes carbon dioxide and a halogenated blowing agent such as hydrofluorocarbon, hydrochlorofluorocarbon, hydrofluoroether, hydrofluoroolefin, hydrochlorofluoroolefin And a co-blowing agent selected from the group consisting of hydrobromofluoroolefins, hydrofluoroketones, hydrochloroolefins, and fluoroiodocarbons, alkyl esters such as methyl formate, water, and mixtures thereof; and ( b) A step of starting foaming of the expandable resin composition.

  In yet another embodiment of the present invention, a method of making a foam composition using a blowing agent composition includes the following steps: (a) mixing a blowing agent and a foamable resin; The step of forming an expandable resin composition, wherein the blowing agent includes carbon dioxide and a halogenated blowing agent such as hydrofluorocarbon, hydrochlorofluorocarbon, hydrofluoroether, hydrofluoroolefin, hydrochlorofluoroolefin And a co-blowing agent selected from the group consisting of hydrobromofluoroolefins, hydrofluoroketones, hydrochloroolefins, and fluoroiodocarbons, alkyl esters such as methyl formate, water, and mixtures thereof; (b) Cooling the expandable resin composition; and (c) the expandable resin The step of extruding Narubutsu.

FIG. 6 is a plot of initial foam density and foam density after 48 hours aging for a foam having an initial density of less than 3.5 pcf.

  Aspects of the invention include blowing agent compositions for making low density, dimensionally stable foams, methods of making the compositions, and methods of using the blowing agents.

  As used herein, the term “foaming agent” includes a physical blowing agent (eg, a dissolved gaseous agent) or a chemical blowing agent (eg, a gas generated by decomposition). I want you to understand. The blowing agent is generally added to the molten polymer, for example in an extruder, and foaming begins under suitable conditions to produce a foamed thermoplastic. The blowing agent causes the resin to expand and form cells (eg, communicating or independent pores). As the resin hardens or cures, the foam is made by trapping the blowing agent in the cell or replacing the surrounding air with the blowing agent in the cell. The blowing agents described herein may be environmentally acceptable (eg, they are generally environmentally safe) as understood by those skilled in the art. preferable.

  As used herein, the term “foam” should be understood to include thermoplastic polymer foam, foamed thermoplastic, foamed resin, and polymer foam, which are used interchangeably. As used herein, “foam (s)” generally refers to the resulting product. The foams may have an open, partially-open, or closed structure, as known to those skilled in the art, where the foam is a semi-connected or independent cell structure. It is preferable that the foam has an independent cell structure. These foams are considered “biodegradable and / or biorenewable thermoplastics” because they are chemically degraded over time, or This is because they are made from renewable resources.

  As used herein, the terms “dimensionally stable” and “dimension stability” are used interchangeably to describe the state of a foam product in its final form. Is. Dimensionally stable foams do not cause cell collapse or “crush” of the foam structure after manufacture (eg, after the foam is manufactured) or are considered minimally affected. It is done. Cell collapse after manufacture can occur at various elapsed times after the foam is manufactured (eg, during the curing process or after some time has passed). The dimensionally stable foam is preferably less than about 50% based on the initial foam volume (or density) after aging, more preferably less than about 20% based on the initial foam volume (or density) after aging, and More preferably less than about 10% based on initial foam volume (or density) after aging, even more preferably less than about 5% based on initial foam volume (or density) after aging, and even more preferably after aging It has a volume (or density) rate of change of less than about 2% based on the initial foam volume (or density). A foam showing a decrease in volume will show a corresponding increase in density.

As used herein, the term “density” should be understood to mean the mass per unit volume of a substance. The “low density” foams described herein generally have a density of about 50 kg / m ³ or less, preferably about 32 kg / m ³ or less, more preferably about 25 kg / m ³ or less. It should be understood that “high density” foam includes higher density foam.

  As used herein, unless otherwise indicated, component or component values of a blowing agent or foam composition shall be expressed in terms of weight percent or weight percent of each component in the composition. The indicated numerical value includes the numerical value at the terminal end.

  In one embodiment of the invention, the blowing agent composition comprises carbon dioxide and a halogenated blowing agent such as hydrofluorocarbon, hydrochlorofluorocarbon, hydrofluoroether, hydrofluoroolefin, hydrochlorofluoroolefin, hydrobromofluoroolefin, Hydrofluoroketones, hydrochloroolefins, and fluoroiodocarbons, alkyl esters such as methyl formate, water, and co-blowing agents selected from the group consisting thereof.

  The blowing agent includes carbon dioxide. Carbon dioxide may be introduced in liquid or gaseous form (eg, a physical blowing agent) or may be generated on-site during manufacture of the foam (eg, a chemical blowing agent). For example, carbon dioxide may be formed by decomposing other components during the production of the foamed thermoplastic. For example, carbon dioxide can be generated by adding a carbonate composition or bicarbonate to the foamable resin and heating during the extrusion process. Since carbon dioxide is a common blowing agent, it is often used as a single blowing agent. It has been previously known that the use of carbon dioxide as a single blowing agent in the production of low density foams often causes cell collapse problems after production. Surprisingly, combining carbon dioxide with other selected co-blowing agents minimizes or avoids the problem of cell collapse after manufacture.

  Accordingly, the blowing agent composition includes a co-blowing agent in addition to carbon dioxide. The co-foaming agent may be a low-emission co-foaming agent. The co-blowing agents are halogenated blowing agents such as hydrofluorocarbons, hydrochlorofluorocarbons, hydrofluoroethers, hydrofluoroolefins, hydrochlorofluoroolefins, hydrobromofluoroolefins, hydrofluoroketones, hydrochloroolefins, and fluoroiodocarbons. , Alkyl esters such as methyl formate, water, and mixtures thereof.

  As used herein, the term “halogenated blowing agent” includes blowing agents that contain a halogen element (Group 17 of the Periodic Table). “Hydrofluorocarbon” and “HFC” are interchangeable terms and refer to organic compounds containing hydrogen, carbon, and fluorine. The compound is substantially free of halogens other than fluorine. “Hydrochlorofluorocarbon” and “HCFC” are interchangeable terms and refer to organic compounds containing hydrogen, carbon, chlorine, and fluorine. “Hydrofluoroether” and “HFE” are interchangeable terms and refer to an organic compound containing hydrogen, fluorine, and one or more ether groups. “Hydrofluoroolefin” and “HFO” are interchangeable terms and refer to organic compounds containing hydrogen, fluorine, and one or more carbon-carbon double bonds. “Hydrochlorofluoroolefin” and “HCFO” are paraphrased terms and refer to organic compounds containing hydrogen, chlorine, fluorine, and one or more carbon-carbon double bonds. “Hydrobromofluoroolefin” and “HBFO” are interchangeable terms and refer to an organic compound containing hydrogen, bromine, fluorine, and one or more carbon-carbon double bonds. “Hydrofluoroketone” and “HFK” are interchangeable terms and refer to organic compounds containing hydrogen, fluorine, and one or more ketone groups. “Hydrochloroolefin” and “HCO” are interchangeable terms and refer to an organic compound containing hydrogen, chlorine, and one or more carbon-carbon double bonds. “Fluoroiodocarbon” and “FIC” are interchangeable terms and refer to organic compounds containing fluorine and iodine.

In embodiments of the present invention, hydrofluorocarbons (HFCs) include the following: HFC-134a (1,1,1,2-tetrafluoroethane), HFC-134 (1,1,2, 2-tetrafluoroethane), HFC-125 (pentafluoroethane), HFC-152a (1,1-difluoroethane), HFC-143a (1,1,1-trifluoroethane), HFC-143 (1,1, 2-trifluoroethane), HFC-227ea (1,1,1,2,3,3,3-heptafluoropropane), HFC-245fa (1,1,2,2,3-pentafluoropropane), HFC -245ca (1,1,2,2,3-pentafluoropropane), HFC-236fa (1,1,1,3,3,3-hexafluoropropaprop ), HFC-365mfc (1,1,1,3,3-pentafluorobutane), HFC-4310mee (1,1,1,2,2,3,4,5,5,5-decafluoropentane), And mixtures thereof. In a preferred embodiment, the HFC is, C ₂ -C ₆ fluorine-containing alkane, preferably a C ₂ -C ₃ fluorine containing alkane. The fluorine-containing alkane may be a linear carbon chain such as fluorinated ethane or fluorinated propane, or it may be a cyclic alkane such as fluorinated propane. In a preferred embodiment, the HFC is HFC-134a (1,1,1,2-tetrafluoroethane), which is nonflammable. In another preferred embodiment, the HFC is HFC-152a (1,1-difluorofluoroethane), which is flammable but has a GWP of less than 150.

The hydro fluoroolefin _{(HFO), C 2 ~C 6} HFO, preferably include C ₃ ~C ₄ HFO. Hydrofluoroolefins (HFO) include in particular the following: HFO-1234yf (2,3,3,3-tetrafluoropropene), HFO-1234ze (E- and / or Z-1,3,3) , 3-tetrafluoropropene), HFO-1243zf (3,3,3-trifluoropropene), HFO-1225ye (E- and / or Z-1,2,3,3,3-pentafluoropropene), HFO -1336mzz (E- and / or Z-1,1,1,4,4,4-hexafluorobut-2-ene), and mixtures thereof. In preferred embodiments, the HFO is HFO-1234yf (2,3,3,3-tetrafluoropropene), HFO-1243zf (3,3,3-trifluoropropene), or HFO-1234ze (E-1 , 3,3,3-tetrafluoropropene).

Hydrochlorofluoroolefin (HCFO) includes C ₃ -C ₆ HCFO, preferably C ₃ -C ₄ HCFO, more preferably chlorofluoropropene and dichlorofluoropropene, and even more preferably monochlorotrifluoropropene. In an embodiment of the invention, the chlorine atom of HCFO is bonded to unsaturated carbon. Particularly as hydrochlorofluoroolefins (HCFO), HCFO-1233zd (E- and / or Z-1-chloro-3,3,3-trifluoropropene), HCFO-1233xf (2-chloro-3,3,3- Trifluoropropene). In a preferred embodiment, the HCFO is HCFO-1233zd (E- and / or Z-1-chloro-3,3,3-trifluoropropene), more preferably trans-HCFO-1233zd (E-1-chloro). -3,3,3-trifluoropropene).

Hydrofluoroethers (HFE) include the following: HFE-125 (pentafluorodimethyl ether), HFE-134 (1,1,1 ′, 1′-tetrafluorodimethyl ether), HFE-143a (1, 1,1-trifluoroethane), HFE-152a (difluoromethyl methyl ether), HFE-245fe2 (1,1,2,2-tetrafluoroethyl methyl ether), HFE-356mff2 (bis (2,2,2- Trifluoroethyl) ether), HFE-7200 (C ₄ F ₉ OC ₂ H ₅ ), HFE-7100 (C ₄ F ₉ OCH ₃ ), and HFE-356 mec (1, 1, 1, 2, ₃ , ₃ , 3-hexafluoro-3-methoxypropane).

  In a preferred embodiment, the hydrochloroolefin includes, for example, trans-1,2-dichloroethylene. Examples of the alkyl ester include alkyl formate. Preferred alkyl formates include, for example, ethyl formate and methyl formate, more preferably methyl formate. A preferred fluoroiodocarbon is, for example, trifluoroiodomethane.

  In one embodiment, the co-blowing agent is a halogenated blowing agent such as hydrofluorocarbon, hydrochlorofluorocarbon, hydrofluoroether, hydrofluoroketone, hydrofluoroolefin, hydrochlorofluoroolefin, brominated hydrofluoroolefin (hydro Selected from the group consisting of bromofluoroolefins), and mixtures thereof. In an exemplary embodiment, the environmentally acceptable co-foaming agent is hydrofluoroolefin and hydrochlorofluoroolefin, and mixtures thereof.

  In an exemplary embodiment, the co-blowing agent is 1,1,1,2-tetrafluoroethane (HFC-134a), 3,3,3-trifluoropropene (HFO-1243zf), 2,3,3 , 3-tetrafluoropropene (HFO-1234yf), trans-1,3,3,3-tetrafluoropropene (trans-HFO-1234ze), trans-1-chloro-3,3,3-trifluoropropene (trans -HCFO-1233zd), and mixtures thereof. In a preferred embodiment, the co-blowing agent is 1,1,1,2-tetrafluoroethane (HFC-134a). In another preferred embodiment, the co-foaming agent is 3,3,3-trifluoropropene (HFO-1243zf). In another preferred embodiment, the co-foaming agent is 2,3,3,3-tetrafluoropropene (HFO-1234yf).

  Particularly suitable co-blowing agents have a low global warming potential (GWP). For example, it is known that hydrofluoroolefins generally exhibit low GWP. Therefore, it is desirable to select a co-blowing agent having a GWP of less than 150, preferably less than 50, more preferably less than 20. In particular, 3,3,3-trifluoropropene (HFO-1243zf), 2,3,3,3-tetrafluoropropene (HFO-1234yf), trans-1,3,3,3-tetrafluoropropene (trans- HFO-1234ze), and mixtures thereof, advantageously have low GWP values. Further, it is conceivable that the co-blowing agent does not contain VOCs (i.e. does not contain volatile organic compounds) or has minimal VOC emission.

  In one exemplary embodiment, the co-blowing agent has a boiling point under atmospheric pressure of less than 30 ° C, more preferably less than 14 ° C. In particular, the co-blowing agent is 1,1,1,2-tetrafluoroethane (HFC-134a), which has a boiling point of −26.3 ° C. (−15.34 ° F.). . In particular, the co-blowing agent is 3,3,3-trifluoropropene (HFO-1243zf), which has a boiling point of about −22 ° C. (−7.6 ° F.). In particular, the co-foaming agent is 2,3,3,3-tetrafluoropropene (HFO-1234yf), which has a boiling point of about −28.5 ° C. (−19.3 ° F.). Yes. In particular, the co-blowing agent is trans-2,3,3,3-tetrafluoropropene (E-HFO-1234ze), which has a boiling point of about −16 ° C. (3.2 ° F.). doing. In order to obtain a blowing agent composition that forms a foam having the desired dimensional stability, it is not necessary to include a co-blowing agent having a higher boiling point.

  As described herein, particularly when carbon dioxide is selected with a co-blowing agent, it is possible to produce dimensionally stable, low density foam products. Low density foams made from known blowing agents or typical combinations of blowing agents have only poor dimensional stability because the volume of the foam decreases over time (i.e. This is because cell collapse occurs). For example, increasing the blowing agent content to 8% by weight with carbon dioxide alone results in a foam that is initially low density but dimensionally unstable and exhibits significant foam cell collapse during aging. In order to produce low density foams using common blowing agents, additives can be combined with the polymer, or the polymer structure can be altered during formation or curing to stabilize the resulting foam structure. Wake me up. Known typical additives that are added to polymer foam to improve dimensional stability include carbon nanoparticles, nanoclay, nanographite, glass fibers, and the like. However, selecting a specific blowing agent as described herein can produce a low density foam with high dimensional stability without any modification or addition to the polymer structure itself. It's been found. Although these low density foams can be made using known combinations of blowing agents, surprisingly, highly stable foams that do not undergo cell collapse after production over time are surprising. can get.

  In particular, the weight ratio of carbon dioxide to co-blowing agent is about (0.1: 1) to (1: 0.01), preferably (0.5: 1) to (1: 0.1), More preferably, a blowing agent composition having a carbon dioxide to co-blowing agent ranging from (0.6: 1) to (1: 0.1) is used to produce a highly dimensionally stable foam. be able to. An appropriate amount of the blowing agent may be determined based on the amount of the resin composition to be used. In one embodiment of the invention, carbon dioxide is present in an amount less than about 15% by weight of the foamable resin composition. In another embodiment, the co-foaming agent is present in an amount less than about 15% by weight of the foamable resin composition. In another embodiment, the co-foaming agent is present in an amount less than about 9% by weight of the foamable resin composition. In a preferred embodiment, carbon dioxide is present in an amount of about 3-15% by weight, preferably 4-12% by weight, most preferably about 5-10% by weight, and the co-blowing agent is about 1-5% by weight. %, More preferably in an amount of about 2-3% by weight. In particular, carbon dioxide should be present in an amount of about 3-8% by weight and co-blowing agent in an amount of about 1.5-5% by weight. In another embodiment, the total amount of blowing agent present is less than about 15% by weight. In another embodiment, the total amount of blowing agent present is between about 5-15% by weight.

  In embodiments of the present invention, foamable, biodegradable or biorenewable resin compositions and carbon dioxide and halogenated blowing agents such as hydrofluorocarbons, hydrochlorofluorocarbons, hydrofluoroethers, hydrofluoroolefins, Blowing agent comprising hydrochlorofluoroolefin, hydrobromofluoroolefin, hydrofluoroketone, hydrochloroolefin, and fluoroiodocarbon, alkyl ester such as methyl formate, water, and a co-blowing agent selected from the group consisting thereof A biodegradable or biorenewable foam is formed from the composition. These resins and foams are considered “biodegradable and / or biorenewable” because they are chemically degraded over time or they are derived from renewable resources. It is because it is manufactured. The biodegradable and / or biorenewable resin may be used as a mixture or blend with an additional polymer that is not considered biorenewable or biodegradable. Such additional polymers include, for example, the following: polyalkenyl aromatic polymers such as polystyrene and styrene-acrylonitrile, polyolefins such as polyethylene and polypropylene, acrylic resins such as polymethyl methacrylate and polyacrylic acid Butyl, and copolymers, and mixtures thereof. The resin of the present invention comprises a biodegradable / biorenewable resin and an additional polymer, preferably about (1: 1) or more by weight ratio of biodegradable / biorenewable resin to additional polymer. More preferably, by weight ratio of biodegradable / biorenewable resin to additional polymer (3: 1) or more, even more preferably biodegradable / biorenewable resin to add It is included in the polymer by weight ratio (9: 1) or more.

  Certain thermoplastics have been found to behave differently with respect to the structural cell collapse of the foam. For example, polystyrene does not show the same degree of cell collapse as polylactic acid. While not wishing to be bound by any particular theory, one difference between the different types of thermoplastics is, in part, that of the blowing agent that can be added to the resin composition. It can be attributed to the amount and how quickly the blowing agent diffuses out of the foam. For example, it is believed that the solubility and diffusibility of carbon dioxide in polystyrene is lower than that of polylactic acid. While not wishing to be bound by theory, it is likely that cell structure collapses when carbon dioxide diffuses out of the foam faster than air enters the foam by diffusion. It can be considered that. Thus, embodiments of the present invention are particularly suitable for use with relatively polar thermoplastics such as polyester (including polylactic acid). Polylactic acid is of particular interest in embodiments of the present invention because it has biodegradable and / or biorenewable properties. Polylactic acid or polylactide (PLA) is a biodegradable thermoplastic aliphatic polyester derived from renewable resources such as corn, starch, or sugar cane.

  Accordingly, suitable biodegradable / biorenewable plastics for use in combination with the blowing agent compositions described herein include, but are not limited to: : Polylactide, especially polylactic acid (PLA); poly (lactic acid-co-glycolic acid); polycaprolactone; starch, especially those with amylase higher than 70%; polyvinyl alcohol; ethylene vinyl alcohol copolymer; polyhydroxyalkanoate; And mixtures thereof.

  In an embodiment of the present invention, the foamable, biodegradable or biorenewable resin composition is selected from the group consisting of: polylactide, poly (lactic-co-glycolic acid), poly Caprolactone, starch, polyvinyl alcohol, ethylene vinyl alcohol copolymer, polyhydroxyalkanoate, copolymers thereof, and mixtures thereof. In an exemplary embodiment, the polymer resin is polylactic acid or an extrusion modified polylactic acid.

  As used herein, the term “polylactic acid” can refer to a polymer or copolymer comprising at least 50 mol% lactic acid monomer component units. Examples of polylactic acid resins include, but are not limited to: (a) homopolymers of lactic acid, (b) lactic acid and one or more aliphatic hydroxycarboxylic acids other than lactic acid. Copolymer of acid, (c) copolymer of lactic acid and aliphatic polyhydric alcohol and aliphatic polycarboxylic acid, (d) copolymer of lactic acid and aliphatic polycarboxylic acid, (e) lactic acid and aliphatic polyhydric alcohol And (f) a mixture of two or more of (a) to (e) above.

  Examples of lactic acid include: L-lactic acid, D-lactic acid, DL-lactic acid, their cyclic dimers (ie, L-lactide, D-lactide, or DL-lactide), and mixtures thereof. . Examples of hydroxycarboxylic acids other than lactic acid in copolymer (b) include, but are not limited to: glycolic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxycaproic acid, and hydroxyheptane acid. Examples of aliphatic polyhydric alcohol monomers useful in the copolymers (c) or (e) described above include, but are not limited to: ethylene glycol, 1,4-butanediol 1,6-hexanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, decamethylene glycol, glycerin, trimethylolpropane, and pentaerythritol. Examples of aliphatic polycarboxylic acid monomers useful in the above copolymer (c) or (d) include, but are not limited to: succinic acid, adipic acid, suberic acid, Sebacic acid, dodecanedicarboxylic acid, succinic anhydride, adipic anhydride, trimesic acid, propanetricarboxylic acid, pyromellitic acid, and pyromellitic anhydride.

The biodegradable or biorenewable foam is a low density foam. In one embodiment of the invention, the biodegradable or biorenewable foam has a density of less than about 50 kg / m ³ . In another embodiment, the biodegradable or biorenewable foam has a density of less than about 32 kg / m ³ . In an exemplary embodiment, the biodegradable or biorenewable foam has a density of less than about 25 kg / m ³ .

  By selecting carbon dioxide and the co-foaming agent described herein, it is possible to produce dimensionally stable, low density foam products. Although these low density foams can be made using known blowing agents in novel combinations, they give highly stable foams that do not undergo cell collapse after production over time. The dimensional stability of the foam can be quantified using the volume change of the foam after a predetermined time. However, foam stability can also depend on the density of the foam. While not wishing to be bound by any particular theory, it is believed that a higher density foam will be more stable than a lower density foam because a higher density foam will have its foam structure This is because it contains more polymer material to form (eg, fewer communicating / independent cells). Therefore, high density foams will often have higher dimensional stability than low density foams. Thus, the volume change rate can vary depending on the density of the foam.

In an exemplary embodiment of the invention, the biodegradable or biorenewable foam is less than about 20% after aging based on the initial foam volume, preferably about 10% after aging based on the initial foam volume. Less than about 5% after aging based on the initial foam volume, and even more preferably less than about 2% after aging based on the initial foam volume. In other words, the increase in density is no more than 20%, preferably no more than about 10%, more preferably no more than about 5%, even more preferably no more than about 2% from the initial density. In particular, for foams having a density of about 25-49 kg / m ³ , the density change after aging is preferably less than about 10%. The initial foam density (or volume) can be determined immediately after the foam is manufactured (eg, initial cured).

  Aging includes placing the foam under certain environmental conditions for a predetermined time. In embodiments of the invention, the volume change is measured by aging the foam under standard conditions for about 40-48 hours. It is preferable that the density (or volume) change rate is minimum, for example, the initial density (or volume) and the final density (or volume) are approximately the same. The density (or volume) may decrease (or increase in volume) after foaming and / or aging. In other words, the density of the foam after aging is higher than the initial foam density. This can happen because at the time of the initial volume measurement, the blowing agent continued to foam and the foam was not yet fully cured. This further uses a combination of blowing agents that is less diffusible than air so that the air diffuses into the foam faster than the combination of blowing agents dissipates from the foam, further expanding the foam. Can also happen. Then, the density change can be from 0% to -2.5%. However, this is undesirable because the density of the aged foam is higher (especially substantially further) than the initial foam density, which results in undesirable cell collapse of the foam structure. Thus, by selecting a combination of carbon dioxide and the co-foaming agent described herein, the volume change after aging is minimized and structural cell collapse is minimized or not at all, It is possible to produce a low density foam that is dimensionally stable.

  As described above, in order to produce a low-density foam using a conventional foaming agent, for example, for the purpose of stabilizing the foam structure obtained, an additive is added to the polymer resin while stirring. It was. However, in exemplary embodiments of the present invention, some foamable, biodegradable or biorenewable resin compositions may be used to maintain the dimensional stability of the biodegradable or biorenewable foam. No additional additives are added or present. Therefore, no component for improving the strength of the polymer foam is added. Similarly, no particular polymer foam is selected for the purpose of providing improved mechanical strength or preventing cell collapse. For example, a conventional polylactic acid resin may be selected, and the foaming agent composition described herein may be used to provide low density, dimensionality without any modification to the polylactic acid resin. A stable foam is produced.

  In one embodiment, additives for improving the dimensional stability of the foam are not used, but other additives may be included in the resin composition. For example, a melt strength modifier may be used for polylactic acid that is not foamable by itself. Alternatively, foam grade polylactic acid may be used that does not require a melt strength modifier to cause foaming. When the non-foaming grade polylactic acid includes a melt strength modifying additive to enable foaming, the melt strength modifying agent improves or maintains the dimensional stability of the resulting foam structure. Not included. It should be understood that the term “foamable” is capable of forming bubbles and does not rupture. In other words, under foaming conditions, the non-foaming grade resin will either not initiate foaming or many of the generated pores will burst quickly. In either case, as a result, the foam structure is never generated. Even if a melt strength modifier is added to make the non-foamable resin a foamable type, the melt strength modifier can maintain or improve the dimensional stability of the foam produced. , I didn't aim or expect. In other words, if a non-foaming grade polylactic acid is combined with a melt strength modifier and a foaming agent composition not in accordance with the present invention (eg, carbon dioxide alone) is used, the foam The structure will still collapse into cells and have poor dimensional stability. However, when the blowing agent composition described herein is selected, it is possible to obtain a low density foam having high dimensional stability regardless of the use of a melt strength modifier.

  The foamable, biodegradable or biorenewable resin composition can include at least one additive selected from the group consisting of: a nucleating agent, a cell regulator, a viscosity modifier. Quality agent, melt strength improver / modifier, lubricant, dye, pigment, filler, antioxidant, extrusion aid, stabilizer, antistatic agent, flame retardant, IR attenuating agent , Additional polymers, and insulating additives, and mixtures thereof. Nucleating agents include in particular substances such as talc, calcium carbonate, sodium benzoate, chemical blowing agents such as azodicarbonamide or sodium bicarbonate, and citric acid. IR attenuating agents and thermal insulating additives include carbon black, graphite, silicon dioxide, metal flakes or powders, among others. Flame retardants include in particular phosphorylated or brominated substances such as hexabromocyclodecane and polybrominated biphenyl ethers.

  In one embodiment of the present invention, the method of making the blowing agent composition comprises carbon dioxide and a halogenated blowing agent such as hydrofluorocarbon, hydrochlorofluorocarbon, hydrofluoroether, hydrofluoroolefin, hydrochlorofluoroolefin, Mixing hydrobromofluoroolefins, hydrofluoroketones, hydrochloroolefins, and fluoroiodocarbons, alkyl esters such as methyl formate, water, and co-blowing agents selected from the group consisting of mixtures thereof. The blowing agent composition can be prepared by various suitable mixing methods known to those skilled in the art. The blowing agent composition may be mixed with the resin composition at the same time, for example, in an extruder during foam production.

  In yet another embodiment of the present invention, a method of making a low density foam using a blowing agent composition includes the following steps: (a) mixing a blowing agent and a foamable resin; A step of forming an expandable resin composition, wherein the blowing agent includes carbon dioxide and a halogenated blowing agent such as hydrofluorocarbon, hydrochlorofluorocarbon, hydrofluoroether, hydrofluoroolefin, hydrochlorofluoroolefin, And a co-blowing agent selected from the group consisting of hydrobromofluoroolefins, hydrofluoroketones, hydrochloroolefins, and fluoroiodocarbons, alkyl esters such as methyl formate, water, and mixtures thereof; and (b) A step of starting foaming of the expandable resin composition. Foaming may be initiated by any suitable method known to those skilled in the art. For example, polylactic acid resin may be supplied to the extruder. The foaming agent composition is added to the polylactic acid resin melted in the extruder, mixed and dissolved to form an expandable resin composition. According to the selected polymer resin, an optimum melting temperature for introducing the foaming agent composition under optimum conditions may be determined. The expandable resin composition may be cooled to a suitable foaming temperature, which can be determined by one skilled in the art for the selected resin. The expandable resin composition is then extruded from the die where it begins to foam due to pressure drop. Foaming may continue until the foaming agent is de-activated or the foam is fully cured.

  Various types of equipment generally known to those skilled in the art may be used to produce the foam. Typically, the foam may be produced using an extrusion system. Such an extrusion system may use a single extruder, two extruders connected in series or otherwise configured. The extruder may be a single screw extruder, a twin screw extruder, or other configuration. The extrusion system incorporates additional equipment, including molds, gear pumps, resin feeders, blowing agent feed pumps, take-up machines, cutting machines, heat exchangers, and other equipment components known to those skilled in the art. It may be. In certain embodiments, a counter-rotating twin screw extruder may be employed. However, it is contemplated that the blowing agent composition may be combined with the resin composition using various means, methods, and equipment used by those skilled in the art. Similarly, the shape of the resulting foam may be any suitable shape manufactured by those skilled in the art, such as rod, brick, sheet, strip, and the like. The foam may have a variety of desirable structures, including bubbles in communicating cells or independent cells. In a preferred embodiment, the foam is primarily a stand-alone cell foam.

  In an exemplary embodiment, a method of using a blowing agent composition to make a foam composition includes the following steps: (a) an expandable resin by mixing a blowing agent and a foamable resin. Forming a composition, wherein the blowing agent includes carbon dioxide and a halogenated blowing agent such as hydrofluorocarbon, hydrochlorofluorocarbon, hydrofluoroether, hydrofluoroolefin, hydrochlorofluoroolefin, hydrobromofluoro A co-blowing agent selected from the group consisting of olefins, hydrofluoroketones, hydrochloroolefins, and fluoroiodocarbons, alkyl esters such as methyl formate, water, and mixtures thereof; (b) the expandable resin Cooling the composition; and (c) the expandable resin composition Extrusion to process.

  The foaming agent composition may be added to the foamable resin in various appropriate states. For example, the blowing agent may be incorporated into the foamable resin in a gas state or a supercritical state. Further, as is generally understood by those skilled in the art, the blowing agent composition may be added as either a physical blowing agent or a chemical blowing agent. In particular, carbon dioxide may be introduced as a physical carbon dioxide source or as a chemical carbon dioxide source. It is preferred that the co-foaming agent is a physical foaming agent. The physical blowing agent is fed to the extruder and added to the resin melt either in the gaseous, liquid, or supercritical state, preferably in either the liquid or supercritical state. In certain embodiments of the invention, carbon dioxide and the co-blowing agent are physical blowing agents. In another embodiment, the blowing agent composition is formed in situ, where the physical blowing agents, carbon dioxide and co-blowing agent, are separately fed to an extruder and into the resin melt. Added, where it is mixed with the resin to form a foamable composition. In yet another embodiment of the invention, prior to mixing with the resin melt, the physical blowing agent, carbon dioxide and co-blowing agent, is fed to a common injection point or mixing apparatus where A foaming agent composition is formed by mixing and then added to the resin melt. In yet another embodiment of the invention, the blowing agent composition is formed during the mixing process, where the co-blowing agent is a physical blowing agent and carbon dioxide is generated from the chemical blowing agent.

  Therefore, a formulation comprising a specific blowing agent composition comprising both carbon dioxide and a selected co-blowing agent such as HFC-134a should be used to produce dimensionally stable, low density foam. . Specifically, using a specific blowing agent combination of carbon dioxide and a selected co-blowing agent such as HFC-134a, manufactured using carbon dioxide alone or in combination with other conventional blowing agents. Dimensionally stable PLA foams may be produced that have a lower density than can be done.

  In yet another embodiment of the invention, a specific blowing agent composition consisting essentially of hydrofluorocarbon (HFC), hydrofluoroolefin (HFO), hydrochlorofluoroolefin (HCFO), and mixtures thereof is used. Thus, a dimensionally stable, biodegradable or biorenewable low density foam may be produced. In particular, HFC-134a, HFC-152a, HFC-245fa, HFC-227ea, HFC-365mfc, and mixtures thereof are used to produce dimensionally stable PLA foams, such as HFC blowing agents. Also good. In particular, HFO foaming agents such as HFO-1243zf, HFO-1234yf, E-HFO-1234zd, Z-HFO-1336mzz, E-HCFO-1233zd, HCFO-1233xf are used to produce dimensionally stable PLA foam. May be. Specifically, dimensionally stable PLA foam may be produced using HFC-134a, HFC-152a, HFO-1243zf, HFO-1234yf, E-HFO-1234ze, and mixtures thereof.

PLA Foam Extrusion To produce a low density foam with improved dimensional stability, the following examples were given. Extruded polylactic acid (PLA) foam was produced using a counter-rotating twin screw extruder with a barrel inner diameter of 27 mm and a barrel length of 40 times the diameter. The pressure inside the extruder barrel was adjusted using a gear pump, and the pressure was set so that the blowing agent composition could be sufficiently dissolved in the extruder. The extruder die was an adjustable-lip slot die with a gap width of 6.35 mm. The foaming experiments used foamable PLA resins for general use, including 4% by weight acrylic copolymer melt strength modifier (available from Arkema Biostrength 700, Arkema, Inc.) and 0.4. It contained wt% talc (nucleating agent). Resin was fed to the extruder at a rate of 4.54 kg / hr (10 lb / hr). The blowing agent was pumped using a high pressure infusion pump, controlling the rate into the PLA resin melt. In the extruder, the blowing agent was mixed with the resin melt and dissolved therein to form an expandable resin composition. When the expandable resin composition was cooled to an appropriate foaming temperature and extruded from the die, pressure drop occurred and foaming started.

  About the foam sample extract | collected in the middle of each experiment, the density and the continuous cell content were measured. The density was measured according to ASTM D792, and the continuous cell content was measured using the gas pycnometer method described in ASTM D285-C. The dimensional stability of the foam sample was calculated as the rate of change of foam volume relative to the initial foam volume as a function of time. The volume of the foam sample was determined using a simple water displacement method.

  The foam samples from the examples of the present invention were in the form of foamed rods. For aging purposes, the foamed rod was cut to a sample length of about 6-10 inches. The samples were stored at ambient conditions and periodically checked for volume and appearance.

Example 1:
Using the above-described method, PLA foam was prepared using 3.2 wt% CO ₂ and 4.4 wt% HFC-134a (1,1,1,2-tetrafluoroethane) as the blowing agent composition. Prepared. After 40 hours of aging, the foam had a density of 40.5 kg / m ³ . There was no noticeable change in the appearance of the foam and there was no end shrinkage.

Comparative Example 1:
PLA foam was prepared using the method described above, except that only 6.9 wt% CO ₂ was used as the blowing agent. The resulting foam had an initial density of 43.6 kg / m ³ . After 40 hours of aging, the foam had a density of 45.5 kg / m ³ . There was also significant end shrinkage.

  The results for Example 1 and Comparative Example 1 are summarized in Table 1.

  As is evident from these results, low density and dimensionally stable foams were produced using the blowing agent compositions according to embodiments of the present invention. There was no noticeable change in the appearance of the foam of Example 1, and there was no end shrinkage.

Examples 2-15 and Comparative Examples 2-7:
Independent cell PLA foam was prepared in the same manner as described above. For each foam sample, the density was measured immediately after foaming to obtain the initial density. The samples were then aged for about 48 hours under ambient conditions before the density was remeasured to determine the density of the aged foam. An increase in foam density (ie, a decrease in sample volume) was an indication of foam cell collapse due to the rapid diffusion of the blowing agent from the sample. In Comparative Example 2-7, the foaming agent was substantially CO _2. In Examples 2 to 4, the blowing agent was substantially HFC-134a (1,1,1,2-tetrafluoroethane). In Examples 5 to 11, the foaming agents were CO ₂ and HFC-134a. In Examples 12 to 15, the foaming agents were CO ₂ and HFO-1243zf (3,3,3-trifluoropropene).

From these examples, if the initial foam density is similar, the foam foamed using only CO ₂ as the foaming agent has CO ₂ and either HFC-134a or HFO-1243zf as the co-foaming agent. It can be seen that the change in density was significantly higher than the foam used or foamed using HFC-134a as the only blowing agent.

The results are further summarized in FIG. 1, where the initial foam density is plotted against the foam density after 48 hours aging for foams with an initial density of less than 3.5 pcf. From FIG. 1, foams prepared using only CO ₂ as the blowing agent experienced a change in foam density of about 10% or more, whereas HFC-134a or HFO-1243zf was used alone or in combination. It can be seen that the foam prepared using as a blowing agent has undergone less than 10% change in density.

Permeation of blowing agent through PLA film From the examples below, the permeation rate of tetrafluoropropene through PLA film is approximately the same as that of 1,1,1,2-tetrafluoroethane (HFC-134a), or You can see that it is lower. The aging of the independent cell foam is related to the permeability of the blowing agent through the film, so that tetrafluoropropene, especially 2,3,3,3-tetrafluoropropene (HFO-1234yf) and trans-1,3,3 , 3-tetrafluoropropene (E-HFO-1234ze), like HFC-134a, can be used in the blowing agent combination of the present invention.

  A PLA film for general use was attached to the gas / membrane permeation cell as a membrane. The high pressure chamber on one side of the membrane was maintained at a constant pressure using the blowing agent to be tested. The low pressure chamber on the other side of the membrane was flushed with a constant rate of helium, but the low pressure chamber was initially free of any blowing agent to be tested. The low pressure chamber was periodically sampled and analyzed by gas chromatography to monitor the concentration of blowing agent in the helium stream, which gives an indication of the permeation rate through the membrane.

Example 16:
The permeation tests described above were performed on HFC-134a and HFO-1234yf using 3.2 to 3.5 mil thick PLA films. The permeation cell was operated using 19 psig blowing agent back pressure (high pressure chamber) at 18 psig. When HFC-134a was used, a steady state concentration of about 1200 ppm was reached on the low pressure side within 2 minutes. When HFO-1234yf was used, a steady state concentration of about 700 ppm was reached on the low pressure side in about 35 minutes, but reached about 50% of the maximum value after about 5 minutes.

  This example shows that under these conditions, the permeation rate of HFO-1234yf through the PLA is lower than that of HFC-134a.

Example 17:
The permeation test described above was performed on HFC-134a and E-HFO-1234ze using a 4.0 mil thick PLA film. The permeation cell was operated at 23 ° C. using 32 psig blowing agent back pressure (high pressure chamber). When HFC-134a was used, a steady state concentration of about 1000 ppm was reached on the low pressure side within 2 minutes. When E-HFO-1234ze was used, a steady state concentration of less than 150 ppm was reached.

  This example shows that under these conditions, the permeation rate of E-HFO-1234ze through the PLA is lower than that of HFC-134a.

  While preferred embodiments of the invention have been shown and described herein, it is to be understood that such embodiments have been provided for illustrative purposes only. Many variations, changes and substitutions will occur to those skilled in the art without departing from the spirit of the invention. Accordingly, the appended claims are intended to cover all such variations within the spirit and scope of the invention.

Claims (19)

A biodegradable or biorenewable foam comprising:
A polylactic acid composition;
Carbon dioxide,
Co-foam selected from the group consisting of 2,3,3,3-tetrafluoropropene (HFO-1234yf); trans-1,3,3,3-tetrafluoropropene (trans-HFO-1234ze) and mixtures thereof blowing agent formed from the composition and <br/>, biodegradable or renewable foam comprising a agent. The biodegradable or biorenewable foam according to claim 1, wherein the carbon dioxide is present in an amount of less than 15% by weight of the polylactic acid composition. The biodegradable or biorenewable foam according to claim 1, wherein the co-foaming agent is present in an amount of less than 9% by weight of the polylactic acid composition. The biodegradable or biorenewable foam according to claim 1, wherein the biodegradable or biorenewable foam has a density of 50 kg / m ³ or less. The biodegradable or biorenewable foam according to claim 1, wherein the biodegradable or biorenewable foam has a density of 32 kg / m ³ or less. The biodegradable or biorenewable foam according to claim 1, wherein the biodegradable or biorenewable foam has a density of 25 kg / m ³ or less.   The biodegradable or biorenewable foam according to claim 1, wherein the biodegradable or biorenewable foam has a density change rate of less than 50% based on the initial foam density after aging.   The biodegradable or biorenewable foam according to claim 1, wherein the biodegradable or biorenewable foam has a density change rate of less than 20% based on the initial foam density after aging.   The biodegradable or biorenewable foam according to claim 1, wherein the biodegradable or biorenewable foam has a density change rate of less than 10% based on the initial foam density after aging.   The biodegradable or biorenewable foam according to claim 1, wherein the biodegradable or biorenewable foam has a density change rate of less than 5% based on the initial foam density after aging. The organism of claim 1, wherein no additional additives are added to or present in the polylactic acid composition in order to maintain the dimensional stability of the biodegradable or biorenewable foam. Degradable or biorenewable foam. The polylactic acid composition is a nucleating agent, cell regulator, viscosity modifier, melt strength modifier, lubricant, dye, pigment, filler, antioxidant, extrusion processing aid, stabilizer, antistatic. The biodegradable or the biodegradable of claim 1, comprising at least one additive selected from the group consisting of an agent, a flame retardant, an IR attenuating agent, an additional polymer, and a thermal insulating additive, and mixtures thereof. Biorenewable form. 13. The biodegradable or biorenewable foam according to claim 12 , wherein the weight ratio of polylactic acid to additional polymer is at least 1: 1. 13. The biodegradable or biorenewable foam according to claim 12 , wherein the weight ratio of polylactic acid to additional polymer is at least 3: 1. 13. The biodegradable or biorenewable foam according to claim 12 , wherein the weight ratio of polylactic acid to additional polymer is at least 9: 1. A method of making a low density foam using a blowing agent composition comprising the following steps:
A foaming agent and polylactic acid are mixed to form an expandable resin composition, wherein the foaming agent is carbon dioxide and 2,3,3,3-tetrafluoropropene (HFO-1234yf); A co-foaming agent selected from the group consisting of 1,3,3,3-tetrafluoropropene (trans-HFO-1234ze) and mixtures thereof; and initiating foaming of the expandable resin composition ,
Including methods. 17. A method of making a low density polylactic acid foam using the blowing agent of claim 16 , wherein the carbon dioxide is introduced as a physical carbon dioxide source or as a chemical carbon dioxide source. 17. A method of making a low density polylactic acid foam using the blowing agent of claim 16 , wherein the generated foam has a density of less than 50 kg / m < ³ >. A method of using a blowing agent composition to make a polylactic acid foam composition comprising the following steps:
A foaming agent and polylactic acid are mixed to form an expandable resin composition, wherein the foaming agent is carbon dioxide and 2,3,3,3-tetrafluoropropene (HFO-1234yf); A co-blowing agent selected from the group consisting of 1,3,3,3-tetrafluoropropene (trans-HFO-1234ze) and mixtures thereof;
Cooling the expandable resin composition; and extruding the expandable resin composition.

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